Personal communication networks are being deployed extensively worldwide using mobile radio systems. Early cellular networks, still in operation, use analogue modulation formats for the radio air interface protocol. These analogue networks exhibit the problem of call saturation in high usage areas. The North American AMPS system is typical of such an analogue system.
To overcome this problem higher capacity air interface protocols using digital modulation format networks have been introduced, oftentimes operating in tandem with analogue networks, providing cellular radio coverage that by both systems. Examples of digital moblie phone networks currently in operation are the PCS1900, DCS1800 and GSM systems, which are national and supra-national standardised radio air interface protocols (AIPs).
Nevertheless, these networks exhibit the problem of not having global operation. To overcome this problem, additional global radio air interface protocols using digital modulation format networks via satellite have been introduced, such as the digital ODYSSEY system. Furthermore, short range cordless networks, such as the digital CT2 version of the US unlicensed UPCS band, or DECT are becoming increasingly employed.
In a large country such as the United States or Canada the early standardised analogue network known as AMPS has reached a fairly universal coverage of the populated North American continent. The newer digital networks tend to be deployed in areas of high usage. A result of this is that there are areas of digital network coverage overlaying a universal analogue network coverage. Additionally different air interface protocol standards of digital networks have been deployed regionally, since different telecommunications operators have developed their own protocols or have developed such protocols in line with national and sometimes international standards authorities, for example, the GSM protocol.
Whilst it is reasonable to suppose that handsets operable for different radio communications protocols are similar from the users point of view, it is not possible, in particular, to use a digital mobile radio for use in an analogue cellular region and vice versa. This stems from the fact that whilst both types of handsets possess antennas, radio front end transmitter, receiver and baseband circuits, they operate on different air interface protocols with different radio carrier frequencies, duplex timing and modulation formats, which are incompatible.
Therefore it can be seen that each individual personal communications system user will need a dual network service for complete coverage. Consequently the user requires a handset that will not only function throughout the coverage area of the specific subscribed-to digital network, but also have a switched alternative mode to operate on the universal analogue network.
There is a likely deployment scenario where the mobile terminal user wishes to access the two communication operating systems. Therefore there is a need for a dual-mode PCS1900/AMPS, PCS/UDCS, PCS/ODYSSEY, DCS1800/GSM, GSM/DECT, DCS1800/DECT, JDC/Handyphone and JDC/ODYSSEY handsets, to name but a few.
The problem of implementing a dual mode handset has been considered to be surmountable by two different approaches: The first solution uses two separate radio transceivers piggybacked and combined at the antenna and at the man-machine interface (keyboard and audio); The second solution uses two separate radio sections piggybacked and combined at the digital signal processing part of the radio transceiver. These two approaches have problems in that they are complicated and unwieldy, and it is clear that a dual-mode radio architecture with an increased functional commonality of circuits would be the most cost effective solution.